A lithographic exposure apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic exposure apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning structure, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic exposure apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning structure to the substrate by imprinting the pattern onto the substrate.
In a lithographic apparatus, coil motors (such as Lorentz-force motors) are used, for example, to position a substrate table and/or a support structure configured to hold a patterning structure (e.g., a mask table). The motors dissipate heat in operation which, if not removed in a controlled manner, could affect the thermal stability of the apparatus. For example, in the case of positioning of a substrate table, heat transfer from the motor to the substrate table should be low. The substrate table is designed to be operated at a certain temperature and heat transfer to the substrate table may lead to expansion or contraction in the substrate table and/or the substrate causing an inaccuracy in the positioning of the substrate and thus of the target portion to which the pattern is to be transferred. Similar considerations may apply to a patterning structure and support structure configured to hold a patterning structure. Thus, heat may form a restricting factor for the performance of the motor. For example, the temperature limit for the motor (does the motor survive the high temperatures?) and/or the heat transfer to other parts (how much heat is transported to the highly accurate patterning device support structure and/or substrate table parts?) may restrict the maximum force. Thus, specific power densities (amount of dissipated heat per unit motor volume) may be limited by thermal specifications.
Similarly, heat transfer considerations may apply to other heat sources whether relating to a lithographic apparatus or not, that may increase the temperature of a structure or environment desired to be kept a regulated lower temperature.